Many MIT CCR members are using vertebrate model organisms to study the role of known or putative cancer genes in both normal development and tumorigenicity. This includes a variety of mutant mouse strains that carry gain-of-function, loss-offunction and/or conditional alleles as well as a large collection of zebrafish strains that carry inactivating viral insertions within numerous genes essential for embryonic development. To support these studies, it is essential that researchers can correctly diagnose the resulting phenotypes and also recover tissue samples to investigate the underlying molecular changes. The Histology Core Facility[unreadable]s mission is to provide CCR researchers with state-of-the-art histological services. The facility carries out the processing and sectioning of tissue samples and the generation of slides on a fee-for-service basis. It also provides cutting-edge intellectual and technical expertise. This includes advice on the generation and fixation of tissue samples and the availability and use of various staining procedures. In addition, a veterinary pathologist, Dr. Roderick Bronson, works in the Facility one day a week. Dr. Bronson is an internationally recognized expert in mouse pathology, and he is available to meet with CCR researchers to assist in the analysis of slides and the diagnosis of developmental and tumor phenotypes. This provides expert training of CCR students, postdocs and staff in histology and has played a significant role in promoting collaborative interactions, both between CCR investigator laboratories and with the wider cancer community, through the identification of shared or related phenotypes in different model systems. The centralization of histological analysis allows the MIT CCR to provide its investigators with a comprehensive range of services while minimizing staff and equipment costs and space requirements. Price comparisons show that the cost to CCR Investigators is highly competitive with those of other academic histology facilities within the Boston/Cambridge area and significantly cheaper than commercial options.